<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <script src="d3.js" charset="utf-8"></script>
    <script>
    window.onload=function (){
      let map=d3.map([
        {name: 'blue', age: 18},
        {name: 'alex', age: 22},
        {name: 'tom', age: 21},
        {name: 'jim', age: 25},
      ], json=>json.name);

      console.log(map.get('blue'));
    };
    </script>
  </head>
  <body>

  </body>
</html>
